I'm a bit new myself... DId you mean the reciever? OR the whole system?
ORIGINAL: dj2_7
I had the same thing happen to me when I was still new at this. I think it's the vibration that causes it. I ended up just buying a new radio for it, beings I wanted a better one anyway. But if you don't want to spend the cash to get a new one I would try to fix it.